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Impact de la pollution atmosphérique par l’ozone sur la communication chimique plante-pollinisateur : le cas de deux interactions emblématiques en Méditerranée

Abstract : Among the pollutants present in the troposphere, ozone (O3) is probably one of the most stressful for organisms, owing to its strong oxidizing potential. For example, high concentrations of O3 ([O3]) can affect the emission of volatile organic compounds (VOCs) that allow plants to communicate with their environment. Moreover, O3 can react with these VOCs in the atmosphere to create new molecules, thus degrading the chemical signals upon which plant-insect interactions, including plant-pollinator interactions, depend. Many studies have shown the effects of O3 on the vegetative parts of plants but very few have studied their effects on their reproductive parts, which are generally responsible for the attraction of pollinators. This work therefore aims to provide knowledge on the effect of O3 in plant-pollinator chemical communication, namely, its effects on (i) the emission of floral VOCs by the plant, (ii) the chemical signal during its transport in the atmosphere and (iii) the recognition of this signal by pollinators.In the Mediterranean region, the interactions between the Mediterranean fig tree, Ficus carica (Moraceae), and its specific pollinator, Blastophaga psenes (Agaonidae), and between the true lavender, Lavandula angustifolia (Lamiaceae), and its generalist pollinator, the honeybee, Apis mellifera (Apidae), are the two emblematic study models chosen to meet the objectives of this dissertation, owing to their specificity and to the frequency and intensity of O3 pollution peaks in this region.This work combined descriptive and experimental studies to determine (i) the daily rate of VOCs emission from flowering plants, (ii) the in natura variation in emission of floral VOCs from fig trees exposed chronically or punctually to O3 pollution and other variables affected by climate change, (iii) the response of plants exposed under controlled conditions to a peak of O3 pollution, in terms of their emission of floral VOCs, (iv) the reaction of O3 with floral VOCs in a controlled atmosphere, and (v) the consequences of these two effects on the attraction of pollinators.The results show that (i) for both models, VOCs emission is correlated with light intensity but also shows different emission peaks during the day, depending on identity of the VOCs; (ii) for F. carica, there is marked seasonal variation in the emission of VOCs in natura, with light intensity, temperature, drought and chronic and acute source of O3 pollution responsible for variations in the emission of floral VOCs; (iii) for both species, exposure under controlled conditions for 5h to 200 ppb O3 (maximum ([O3] recorded in the last 15 years in the Mediterranean region) has no immediate effect on emission of floral VOCs, but (iv) floral VOCs alone exposed to different [O3] react differentially with the pollutant to form new molecules, thus modifying the proportions of VOCs in the mixture at [O3] as low as 40 ppb, and finally, (v) in F. carica, these modifications of VOCs significantly inhibit the attraction of the specific pollinator. This study highlights sources of variation in floral VOC emission in the two model species but also provides an integrative view of the effect of acute exposure to high [O3] on the concentration of VOCs around these plants. Behavioral tests with different pollinators are now essential to characterize the resilience of these interactions to the [O3]-induced variations in VOCs highlighted in this study. More generally, this work points to the importance of studying factors of climate change co-occurring in natura, including the effects of the concentrations of different air pollutants, on chemical communication in different plant-pollinator interactions in order to define measures to protect these interactions in the face of current and future environmental changes.
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Submitted on : Wednesday, May 11, 2022 - 11:33:33 AM
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Candice Dubuisson. Impact de la pollution atmosphérique par l’ozone sur la communication chimique plante-pollinisateur : le cas de deux interactions emblématiques en Méditerranée. Sciences agricoles. Université Montpellier, 2022. Français. ⟨NNT : 2022MONTG001⟩. ⟨tel-03664708⟩

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